Sheet molding compound (SMC) is a workhorse composite — in the form of a tough, thermosetting, B-staged, compression moldable sheet-form molding compound — used commercially since the early 1960s. However, as compounders extend technology to more novel resins, reinforcement types and formats, SMC is being reinvented. With new kinds of SMC come new application opportunities, as with a new product developed by Mitsubishi Chemical Corp. (Tokyo, Japan) with engineering support from Gemini Composites LLC (Seattle, Wash., U.S.), which Mitsubishi acquired in 2017. Called forged molding compound (FMC), the material is an advanced SMC reinforced with chopped carbon fiber and developed for structural applications with fairly complex designs using a compression molding variant.
Highly moldable, isotropic and better performing
FMC edges closer to prepreg performance while retaining more of SMC’s processability and affordability. It combines industrial-grade carbon fiber tows, which are chopped and split into smaller bundles, then impregnated with vinyl ester (VE) or epoxy matrices. By splitting larger tows into finer bundles, it’s possible to achieve materials with better and more uniform mechanical performance at lower cost than starting with aerospace-grade tows. Cure occurs in 40-120 seconds at 130-150°C.
“While there are many different continuous carbon fiber composites, they have limited application,” explains Koichi Akiyama, president, Gemini Composites and one of the developers of FMC. “What we wanted to create was a high-performance, chopped carbon fiber material that could be used in a much wider variety of applications and formed on commonly available equipment. FMC technology really consists of three factors. It involves an advanced material, an optimized molding process and dedicated design. Together, these factors enable FMC to replace lightweight metals in structural applications at significantly lower weight.”
Interestingly, technologies that would prove key to FMC development began as separate research projects around 2015. Initially, the team’s focus was on increasing the performance of Mitsubishi’s own 3K and 15K chopped carbon fiber SMC (CF-SMC) rather than developing a new material. The goal was to produce a true isotropic composite with chopped fibers in complex shapes that offered mechanical performance closer to prepreg.
“Nothing was easy about trying to find ways to use chopped carbon fiber composites in structural applications with complex geometry at an affordable cost,” recalls Akiyama. “However, we were convinced that if we could find the right combination of material, process and design, then what had previously been impossible would become possible.”